Electronic controllers such as thermostats and fan controls are used to control a variety of heating, ventilating and air conditioning (HVAC) equipment as well as other fuel and power consumption equipment. Furnaces, heat pumps, gas burners, water heaters, electric radiators, water radiators, air conditioners, chillers, fans, blowers and humidity controllers are example types of equipment for which electronic controllers are used. These equipment types are often grouped into the category called “HVAC.” Controllers for these equipment types are often located in user-accessible locations that are remote from the controlled equipment. For instance, thermostats are commonly placed on interior walls of a dwelling and located remotely from controlled HVAC equipment that is located, for example, in a utility room or a basement. Typical controllers accept user inputs received via keypads or other input devices and use the inputs to generate control outputs for controlling HVAC equipment and other equipment types. Often, the controller also includes and/or is coupled to a temperature sensor and accepts temperature set point inputs. Control signals are sent to HVAC equipment as a function of the set point inputs and an output from the temperature sensor. For instance, when a furnace system is in a heating mode, a signal calling for heat is sent to the furnace in response to sensing that a temperature is lower than a set point.
Residential and industrial HVAC type applications rely upon utility providers to supply the electricity and/or fuel required for operation of HVAC equipment. One challenge confronting such utility providers today is the great variance in total demand on a network between peak and off-peak times during the day. Peak demand periods are intervals of very high demand on power generating equipment or on fuel supply where load shedding may be necessary to maintain proper service to the network. These periods occur, for example, during hot summer days occasioned by the wide spread simultaneous usage of electrical air conditioning devices or during the coldest winter months in areas where a strong heating load is required.
Another characteristic of utility supply and usage (e.g., electric and/or fuel usage) is the variance in cost of the utility being supplied under different conditions. For instance the cost of providing a utility can increase during peak supply times due to a variety of conditions. The efficiency of power generation or fuel supply equipment, limitations in a utility distribution network, economical cost/demand relationships and other factors all affect utility costs. In this regard, certain customers are amenable to relinquishing the control of their utility requirements as a function of cost, and certain utilities preferably charge for services as a function of the time at which usage occurs.
Several basic strategies and devices have been utilized for controlling HVAC equipment in order to limit the peak power demand on the power and fuel generating capacity of utility companies. One such approach involves sending signals from a utility to disconnect or interrupt the use of certain selected HVAC loads (e.g., air conditioning compressors) when demand has reached a certain point. Another approach involves assuming control of a setpoint function of a thermostat associated with HVAC equipment. The overriding control functions cause the setpoint to change to use less power or fuel at times of high demand or high unit cost.
Such approaches can be implemented for reducing power or fuel consumption during peak demand times or other times when the reduction in utility usage is desirable, such as during periods when the power and/or fuel cost per unit is high. However, typical energy-reduction implementations involve the installation of control equipment at the HVAC equipment, such as by directly coupling a controller to a furnace. This installation of control equipment has often required that skilled technicians physically install the control equipment at its location, which also often required that the technician have access to a customer environment (e.g., access to a customer's home). In addition, typically installations of this type often require a significant amount of technician time, which can be expensive.
Accordingly, the above-discussed issues have been challenging to the implementation of a variety of devices and systems involving climate control and particularly involving the control of HVAC and other equipment in response to price and/or demand conditions.